There have conventionally been well-known a high-pressure mercury lamp and an excimer discharge lamp as a light source device using a gas discharge. Also, a gas discharge device using an ultraviolet light-emitting phosphor has been well-known as an ultraviolet light-emitting source (for example, see Patent Document 1). Further, an external electrode type gas discharge device having a thin tube configuration suitable for a configuration of a flat light source has also been well-known (for example, see Patent Documents 2 and 3).